Integrated circuits (ICs) and other electronic devices often include arrangements of interconnected field effect transistor (FET) devices, also called metal-oxide-semiconductor field effect transistors (MOSFETs). A typical FET device includes a gate electrode as a control electrode, and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power transistor devices are designed to be tolerant of the high currents and voltages that are present in switching applications that previously relied upon electromechanical switches. In a conduction (or ON) state, power transistor devices may handle currents that range from several Amperes to several hundred Amperes. The applications may also involve the power transistor devices blocking high voltages during an OFF state, e.g., 25 Volts or more, without breaking down.
One type of power transistor device is a trench FET device. In trench FET devices, the gate electrode is disposed in a trench to form a vertical channel. Unfortunately, trench FET devices are often configured to block high voltages in only one direction between the source (top) and drain (bottom) electrodes. The power transistor device may breakdown at a much lower voltage level if biased in the other direction.
Efforts to develop trench FET devices for bi-directional switch applications have presented tradeoffs. In some cases, the breakdown voltage in one direction may be improved at the expense of a lower breakdown voltage in the other direction. Another tradeoff is between breakdown voltage and the on-state resistance of the device. For example, the breakdown voltage in one or both directions may be improved by increasing the distance between the source and drain electrodes. However, the increased distance establishes a longer conduction path for the device, which leads to an undesirable increase in the on-state resistance.